This invention relates to an apparatus and method for altering the tension to which a clampband is subjected such that the tension may be reduced after the events requiring high clampband tension conclude, but before clampband separation.
It is sometimes necessary to join various elements, at least temporarily, by clampbands. A clampband is generally made of one or more interconnected segments separated by respective openings. Typically, a connector extends across each opening in the clampband to allow the clampband to be tightened or loosened around the joined elements to be joined. The connector that extends across a respective opening may have various forms depending upon the application of the clampband.
To join elements, a clampband is placed around the abutting end portions of the elements and the clampband is tightened to exert enough tension to hold the elements together under the forces to which the elements are subjected. Typically, a respective fitting is mounted to the end portion of at least one element. Thus, the clampband can extend around and engage the fitting(s) so as to securely join the elements when subjected to the anticipated forces. The forces include, for instance, the weight of the elements and the forces exerted on the elements during their movement. For example, the clampband around the fitting must be tight enough to prevent the forces acting on the elements during movement from detaching the elements. In the aerospace industry, for instance, the elements joined by a clampband are generally heavy and subject to significant forces during movement, particularly during the take-off or launch. Specifically, a satellite launch vehicle, which is joined to a satellite by a clampband, is capable of lifting 2,000 to 31,000 pounds. In addition, the satellite and the launch vehicle are subject to significant forces during the launch process due to high inertial loads and acceleration of thrust. Thus, the connector that extends across the opening in the clampband utilized in satellite applications must tighten the clampband around the satellite and the launch vehicle to the extent necessary to securely join the elements and withstand the substantial forces acting thereupon.
In certain applications, clampbands are designed such that they may be released at a chosen time to purposefully separate the elements. The clampband release procedure may be manual or automated. To release the clampband, the clampband must be expanded and/or opened in some manner. Typically, releasing the clampband involves lengthening or detaching the connector that extends across the opening in the clampband. In the aerospace industry, for example, clampbands may be used to temporarily join launch vehicles to payloads, such that the launch vehicle may separate from the payload once it completes its function. Specifically, during the launch of a satellite, a clampband joins the satellite to the launch vehicle and once the launch vehicle transports the satellite to the desired location for orbit, the launch vehicle must separate from the satellite. One conventional clampband separation method is to cut the connector that extends across an opening in the clampband. Typically, the clampband includes a proximate automated cutter that is attached to a clampband segment, such that the connector may be cut and the clampband separated at a chosen time. At the time the connector is cut, the sudden tension release by the clampband creates a shock to the elements. The tighter the clampband is applied to the fitting(s) between the elements, the higher the tension the clampband exerts upon the fitting(s), and the larger the shock experienced by the elements upon clampband separation. Thus, elements that are heavy and/or that are subject to significant forces during movement, which must be held together temporarily by a clampband, experience a large shock upon clampband separation because of the tightness of the clampband.
If the elements include or contain equipment that is sensitive to sudden movement, then the shock created upon clampband separation may damage the equipment, particularly if the clampband is tightly attached to the fitting(s) between the elements. The shock created upon clampband separation is particularly problematic for satellites, which contain highly sensitive sensors and antennas, in addition to other precision equipment. The shock may damage the sensitive and expensive electronics of the satellite, which may decrease the effectiveness of the satellite or render the satellite useless.
In many applications, including the satellite example, the high tension of the clampband is necessary for only part of the period the elements are joined by the clampband because the forces exerted upon the elements may vary throughout the period. During the launch of a satellite, for instance, high tension in the clampband that joins the satellite and launch vehicle is necessary only during the initial launch period. In the initial launch period, the satellite and launch vehicle experience high inertial loads and acceleration, which necessitates high clampband tension to prevent the satellite from separating from the launch vehicle. The forces on the satellite and launch vehicle, however, are greatly reduced once they exit the earth""s atmosphere. As such, by the time the clampband separates, it is not necessary that the clampband have such high tension. Nevertheless, without a way to reduce the tension of the clampband, the separation of the clampband will create a substantial shock that may damage the sensitive equipment in the satellite. Because there is currently no way to repair an orbiting satellite, the damage will likely result in the loss of a costly satellite.
Thus, there exists a need in the industry for a low cost apparatus that allows a gentle alteration in clampband tension such that the tension may be reduced after the need for high clampband tension no longer exists, but before clampband separation. An apparatus that allows a reduction in clampband tension would decrease the shock experienced by the elements joined by the clampband upon clampband separation and, therefore, reduce the risk of damage to sensitive equipment or electronics contained in the elements.
The present invention is directed to a releasable clampband apparatus and an associated method for altering the tension in a clampband. As such, the releaseable clampband apparatus and the associated method permit the clampband tension to be reduced prior to separation in order to decrease the shock sustained by the elements joined by the clampband upon its separation. The releaseable clampband apparatus includes a discontinuous clampband having at least one opening, a connector, a housing and a moveable positioning assembly. The connector is fixed to one side of an opening in the clampband and extends across the opening of the clampband. The housing is fixed to the other side of the opening in the clampband and has a cavity surrounding at least a portion of the connector. The moveable positioning assembly is at least partially disposed within the cavity of the housing and is connected to the connector such that movement of the moveable positioning assembly with respect to the housing alters the tension of the clampband by varying the size of the opening.
The releaseable clampband apparatus also may include a first piston body connected to the connector as part of the moveable positioning assembly. The first piston body may be sized and shaped to fit at least partially within the cavity of the housing. The first piston body also may have an aperture through which the connector extends.
A second piston body also may be included in the moveable positioning assembly. The second piston body may be sized and shaped to cooperate with the first piston body such that the second piston body also fits at least partially within the cavity of the housing. In addition, the moveable positioning assembly may have at least one pin extending between the first and second piston bodies. The pin may be adapted to change in length. Changing the pin length changes the position of the first and second piston bodies, which, in turn, causes the connector to move relative to the housing.
The releaseable clampband apparatus of one embodiment also includes a heating element that is disposed in thermal contact with at least one of the first and second piston bodies. As such, the pin may be made of a shape memory alloy, which changes in length depending upon whether it is subjected to heat. When the pin is heated, it may reduce in length to move the first and second piston bodies closer together. As the piston bodies move closer together, they slide further into the cavity of the housing. Because the connector moves in conjunction with the piston bodies, it correspondingly moves through the housing to increase the length of the connector across the opening in the clampband and, thus, reduce the tension in the clampband. To facilitate movement of the moveable positioning assembly relative to the housing, embodiments of the present invention may include at least one side of at least one of the first and second piston bodies facing the housing that may be inclined for engaging a correspondingly inclined wall of the cavity of the housing.
Therefore, to initially place the clampband around the elements, the moveable positioning assembly is built with a mechanically stretched pin or pins, is placed within the housing attached to one side of the opening in the discontinuous clampband, and surrounds one end of the connector. The other end of the connector may be loosely fixed to the other end of the discontinuous clampband, such that the clampband components may be assembled prior to placing the clampband around the elements, and the clampband may slide over at least one element to get to the joint where the clampband belongs. Alternatively, the clampband components may be assembled as they are placed around the joint. Sufficient torque is then applied to the connector to tightly fix the connector to each side of the opening in the discontinuous clampband and create clampband tension by decreasing the circumference of the clampband. Thus, the elements are tightly engaged by the clampband during the initial steps of movement, such as a flight, when the elements are subject to significant forces. During the later stages of the flight, when the forces exerted upon the elements decrease, the mechanically stretched pin(s) are heated to decrease the length of the pins, which increases the portion of the connector extending across the opening in the clampband and loosens the clampband while still retaining the elements. Finally, the connector of the loosened clampband is cut to separate the clampband once the elements no longer need to be joined.
The apparatus and method of the present invention provide a low cost and effective technique to gently alter clampband tension, such that clampband tension may be reduced after the need for high clampband tension is no longer present, but before clampband separation. Thus, the present invention protects sensitive and/or expensive equipment or electronics contained in the elements joined by the clampband from excessive shock upon clampband separation, which could cause damage to the equipment or electronics and result in the loss of a costly satellite.